1. Field of the Invention
This invention relates to a liquid crystal cell with two flat glass plates aligned parallel to one another and at a distance from one another, a web of low-melting glass solder provided between the glass plates, a liquid crystal substance provided in the inner space formed by the glass plates and the glass solder web and with electrodes applied on the surfaces of the glass plates facing one another, the connections of which are brought out of the inner space via the glass solder web, and a process for the production of such a liquid crystal cell.
2. Description of the Prior Art
A liquid crystal cell of the above-mentioned type is known from U.S. Pat. No. 3,995,941. Such cells are manufactured nowadays mainly as optical polarization modulators with a twisted nematic liquid crystal substance, such as is stated for example in DT-OS No. 2,158,563. In the bulk manufacture of such rotated crystal cells the glass plates provided with the electrodes are printed on the edge preferably with a solder paste containing a lead borate solder and an organic binder and are soldered at about 500.degree. C. after aligning the glass plates in relation to one another.
By means of various known processes, such as rubbing, oblique vaporizing, the liquid crystal molecules resting on the glass plate are aligned in a preferential direction. For most applications a small angle of incidence, that is to say the angle between the axis of the rod-shaped liquid crystal molecule and its projection on the surface of the plate, is advantageous. Under all circumstances it must be avoided that the angle of incidence varies over the surface of the cell, for example between the parts covered by electrodes and the parts not covered by electrodes.
Such cells when observed from a non-vertical point of view generally project a background which is not homogeneous or electrodes which are visible, even when they are in a condition which is not electrically switched on.
In cells produced according to prior art it frequently occurs that the angle of incidence on the electrode-covered parts of the glass plate is higher than on the parts which are not so covered. This leads to unacceptable optical properties and to a shortened working life of such cells. In principle the effect can be reduced by a coating of the glass plate and the electrodes with a high-quality protective layer, for example 2000 A SiO.sub.2, applied by electron beam vaporization in a very good vacuum. Such protective layers, however, are expensive and there is a need for a cheaper process.